1. Field of the Invention
The invention relates to a process for adding feedstock and catalyst to a high pressure reaction vessel, such as that employed in an ebullated bed process for hydrotreating petroleum derived hydrocarbon distillate fractions. The invention also relates to a control system for adding a catalyst slurry to an ebullated bed reaction vessel.
2. Description of Other Related Methods In The Field
The ebullated bed process comprises the passing of concurrently flowing streams of liquids or slurries of liquids and solids and gas upwardly through a vertically elongated cylindrical vessel containing a catalyst bed. The catalyst in the bed is maintained in random motion in the liquid and has a gross volume dispersed through the liquid greater than the volume of the catalyst when stationary. This technology has been used commercially in the upgrading of heavy liquid hydrocarbons or converting coal to synthetic oils.
The process is generally described in U.S. Pat. No. Re. 25,770 to Johanson incorporated herein by reference. A mixture of hydrocarbon liquid and hydrogen is passed upwardly through a bed of catalyst particles at a rate such that the particles are forced into random motion as the liquid and gas flow upwardly through the bed. The random catalyst motion is controlled by recycle liquid flow so that at steady state, the bulk of the catalyst does not rise above a definable level in the reactor. Vapors along with the liquid which is being hydrogenated are removed at the upper portion of the reactor.
The ebullated bed process has been found to be applicable to hydrocracking petroleum derived hydrocarbon distillate fractions. U.S. Pat. No. 5,108,580 to G. Nongbri et al. teaches the ebullated bed hydrocracking of a heavy vacuum gas oil fraction. This distillate fraction is recycled to extinction between an ebullated bed hydrocracker and a fluid catalytic cracker (FCC).
U.S. Pat. No. 4,744,877 to R. P. Van Driesen et al. teaches a process for adding and withdrawing catalyst from a high pressure reactor which is particularly suited to an ebullated bed reactor. Fresh catalyst is mixed with a transport oil such as light gas oil to form a slurry. The slurry is pumped into the reactor at a predetermined flow rate under flow control (col. 4, lines 17-18).
U.S. Pat. No. 3,398,085 to T. M. Engle teaches a method of adding catalyst to an ebullated bed reactor. Catalyst inventory is controlled either continuously or intermittently.
Related improvements in the art include U.S. Pat. No. 3,523,888 to N. C. Stewart et al.; U.S. Pat. No. 3,410,792 to R. P. Van Driesen et al.; U.S. Pat. No. 3,410,791 to L. A. Perry et al.; and U.S. Pat. No. 3,336,217 to E. P. Meaux.
The related art teaches the adding of catalyst to an ebullated bed reactor in a residuum hydrocracking process with the aid of a discrete slurry oil. There is a need in the art for a method of adding catalyst to an ebullated reactor in a distillate hydrocarbon hydrotreating process.